.
Means Nonprinting, Reset, Decimal Point or Any Character (in Regexp)
The most common use of a period is as a decimal point in line numbers: 12.3.
Visual, Qzmodify and List $char use a period to represent nonprinting characters in displays.
A period as a command at the Visual home line means "reset the current Cut and Paste task".
A period or dot (.) in regular expressions is a placeholder for any character.
/list "[a.c]" (regexp) {one character between "a" and "c"}